Hi, In most dental x-ray machines the tube and the transformer are contained within the head. The head will have two connections from the mains supply via some form of timer.Usually the timer switches the mains on to both the filament and HT transformer at the same time. As a result the filament lights at the same time as the HT is applied. Is the noise coming from the head? If you tilt the head from side to side can you hear oil splashing? If the answer to either of these questions is yes then the tube may be arcing over or broken.
